1. Field of the Invention
The present invention relates to an image fixing device of an image forming apparatus, and more particularly, to an image fixing device of an image forming apparatus implementing a heating roller to apply heat to an image developed on a printing paper to fix the developed image by using a heat pipe.
2. Description of the Related Art
Generally, a copy machine, a printer, a facsimile, and a combination of these machines or the like all perform a printing function and are generally referred to as image forming apparatuses.
The image forming apparatus forms an electro-static latent image by exposing image data fed from an outside to a photoconductor, develops the formed electro-static latent image using a developing agent, and transfers the developed image onto a printing paper. The image forming apparatus fixes the transformed image to the printing paper by using an image fixing device thereof, and discharges the printed paper.
This kind of image fixing device fixes an image to the printing paper by applying heat and pressure to the paper with an image formed thereon.
FIG. 1 is a diagram showing a part of a conventional image forming apparatus employing an image fixing device. Referring to FIG. 1, the conventional image forming apparatus 100 includes an image fixing device 110, an electric power supplier 120 and an engine controller 130. The image fixing device 110 includes a heating roller 112 and a pressure roller 114.
The heating roller 112 has a multiple layer structure of 2 or 3 layers, and applies heat to a printing paper having an image formed thereon (shown in a thick solid line) to fix the image to the paper. The heating roller 112 is equipped with an internally installed induction heating coil 112a. The induction heating coil 112a generates a magnetic field by an AC electric power supplied by the electric power supplier 120.
The magnetic field generated by the induction heating coil 112a generates induced current on the inner surface of the heating roller 112, thereby generating a Joule's Heat. The heating roller 112 is equipped with an externally installed thermistor 112b to detect a temperature of the heating roller 112 heated by the induction heating coil 112a. 
The engine controller 130 controls an electric power supply to the heating roller 112 in response to the temperature detected by the thermistor 112b. 
The pressure roller 114 rotates as if it is in contact with the heating roller 112 to apply a pressure to the printing paper with the image transferred thereto, thereby fixing the image to the paper. The heating roller 112 and the pressure roller 114 rotate respectively in the arrowed directions as shown in FIG. 1, to discharge the printed paper.
However, the conventional heating roller 112 has a difference in temperature between both ends and a center thereof, and the difference in temperature reduces fusing efficiency. That is, cooling times required to cool the ends and the center of the induction heating coil 112a to a predetermined temperature differ from each other. Also, AC magnetic fields occurring around the ends and the center differ from each other, thereby deteriorating the fusing efficiency of the image.
As a result, the conventional heating roller 112 lacks a uniformity of temperature along the longitudinal direction thereof, while having a uniform temperature in the circumferential direction.